In modern society, electronic taps, such as infrared sensing taps, are more and more popular in public places. A user can only put the hand below the tap and water will automatically flow out. Traditional electronic taps have only one mode of electronic outlet. Once the electronic system fails, the tap cannot be used. Failure can be avoided if the electronic tap further has a mechanical outlet switch. Moreover, the traditional electronic tap cannot be turned off. When washing the wash basin or the tap, the tap will be always turned on because of the infrared sensing, which causes water wasting.
In addition, baking, cooking, making tea or coffee are necessary in daily life. Especially in western-style baking, there are strict rules to the ingredients and the flow of water. A user usually needs a measuring cup to get the water. It often happens that when the user takes the measuring cup under the tap to get the water, the measuring cup is filled up in one second when in high flow volume, thus far exceeding the needed volume, which may waste the water. When in low flow volume, the water is acquired slowly, and during the process, the user needs to take care of the volume in the cup to turn off the tap, which is a waste of time and labor. To solve the problems, a rationed tap exists in the market. This rationed tap can supply rationed flow volume according to the setting. The tap is turned off after the flow volume reaches the preset value, so that the user need not take care of the volume. However, existing rationed tap water usually has a flow adjusting portion. The user adjusts the proper flow volume and the water flows out. But mis-operation may happen as the user adjusts the flow volume, whereby the user is not ready to get the water but water still flows out of the tap, causing an inaccurate amount of the water volume to be delivered.